Wiring circuit board having bumps and method of producing same

ABSTRACT

A method of manufacturing a wiring circuit board having bumps is disclosed in which a stable bump connection is possible, and complex operations such as plating pre-treatment are unnecessary. Bumps having a surface roughness on the tip face thereof of 0.2 to 20 μm are formed by forming an etching mask for bump formation on bump formation surface of a metal foil which has a thickness (t 1 +t 2 ) which is the sum of a thickness t 1  of a wiring circuit and a height t 2  of bumps to be formed on wiring circuit and which has a surface roughness of the bump formation surface thereof of 0.2 to 20 μm, and half etching the metal foil from the side of the etching mask for bump formation to a depth corresponding to the desired bump height t 2.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wiring circuit board having bumps,where the bumps are of a uniform height, and a method of manufacturingthe same.

2. Description of the Related Art

Microscopic bumps (for example, bumps being a diameter of 50 μm and aheight of 30 μm) are widely used when connecting electronic componentssuch as a semiconductor device and a liquid crystal display device to awiring circuit board, or when connecting the layers of a multi-layerwiring board.

A typical method of forming bumps of this size is shown in FIGS. 5A to5E.

Specifically, first, as shown in FIG. 5A, a 2 layer flexible board 53 ismade up of a polyimide film 51 on a copper toil 52, and copper toil 52is patterned by photolithography to form a wiring circuit 54 (FIG. 5B).

Next, a cover coat layer 55 is formed on wiring circuit 54 in accordancewith conventional methods (FIG. 5C). For example, cover coat layer 55can be formed by forming a polyamic acid layer on wiring circuit 54,patterning by photolithography, and imidization. Alternatively, a resistink may also be printed thereon.

Next, the area on polyimide film 51 that corresponds to wiring circuit54 is irradiated with laser light to form bump holes 56 (FIG. 5D). Then,after covering cover coat layer 55 with a protective film as needed (notshown in the Figures), microscopic bumps are formed by growing metalbumps 57 by means or electrolytic plating on the portions of wiringcircuit 54 that are exposed in the bottom of bump holes 56 (FIG. 5E).

However, when opening bump holes 56 by means of laser irradiation, thereis a problem with variations in open space due to variations in theamount of smear adhered to the bottom of bump holes 56, and as a result,there is a problem with large variations developing in the height ofmetal bumps 57. Because of this, stable bump connections are difficult.In particular, connecting semiconductor devices to the wiring circuit inone batch by means of ultrasound is difficult. In addition, a platingpre-treatment Is essential in order to improve the strength of theadherence between wiring circuit 54 and the metal bumps 57 formedthereon.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the aforementionedproblems in the prior art, make stable bump connections possible, and toprovide a method of manufacturing a wiring circuit board with bumps thatmakes complex operations such as plating pre-treatment unnecessary.

The present inventor has discovered that bumps with a uniform height anda surface roughness on the tip faces thereof of 0.2 to 20 μm can beformed by half etching a metal foil with a surface roughness of 0.2 to20 μm and a thickness that is the sum of the thickness corresponding tothe height of the metal bumps and the thickness of the wiring circuitlayer, to a depth corresponding to the desired thickness of the metalbumps, without performing complex operations such as platingpre-treatment, and thus stable bump connections can be realized. Thepresent inventor has finally achieved the present invention.

Specifically, the present invention provides a wiring circuit boardhaving bumps in which a cover coat layer is formed on a first side of awiring circuit, an insulating layer is formed on a second side of thewiring circuit, and bumps in continuity with the wiring circuit areformed such that they project from said insulating layer, wherein thewiring circuit and bumps are integrally formed from one metal foil, anda surface roughness of the tip faces of the bumps is 0.2 to 20 μm.

In this wiring circuit board having bumps, it is preferred that ametallic thin film layer consisting of a metal different from the metalfoil is provided between a bump formation surface on the wiring circuitand the insulating layer, in order to improve the adhesive strengthbetween the insulating layer and the metal foil. In particular, in theevent that the insulating layer is a polyimide layer imidized from apolyimide precursor layer, it is preferred that the metallic thin filmlayer exhibits an adhesive strength to the polyimide precursor layerthat is higher than the metal foil. In this way, the adhesiveness withthe polyimide precursor layer (and the imidized layer) can be improved.A combination of copper foil for the metal foil, and a thin film of Ni,Zn, Sn or Ni—Co alloy and the like for the metallic thin film layer canbe preferably mentioned as a combination for this type of metal foil andmetallic thin film layer.

In addition, it is preferred that the cover coat layer has a connectionaperture that allows access to the wiring circuit from the cover coatside.

In addition, the present invention provides a method of manufacturing awiring circuit board having bumps in which the bumps formed on thewiring circuit have a surface roughness on the tip fares thereof of 0.2to 20 μm, the manufacturing method comprising the steps of:

(a) laminating a protective film on a bump formation surface of a metalfoil having a surface roughness of 0.2 to 20 μm and a thickness which isthe sum of a thickness of the wiring circuit and a height of the bumpsto be formed on the wiring circuit, and forming an etching mask forwiring circuit formation on a wiring circuit formation surface of themetal foil;

(b) half etching the metal foil from the side of the etching mask forwiring circuit formation to form a wiring circuit with a desiredthickness;

(c) providing a cover coat layer on the wiring circuit after removingthe etching mask for wiring circuit formation;

(d) forming an etching mask for bump formation on the bump formationsurface after removing the protective film provided on the bumpformation surface of the metal foil;

(e) half etching the metal foil from the side of the etching mask forbump formation to form bumps of the desired height;

(f) forming a polyimide precursor layer to cover the bumps afterremoving the etching mask for bump formation; and

(g) etching back the polyimide precursor layer and imidizing the same toform an insulating layer with a desired thickness. In this method ofmanufacturing, the wiring circuit is formed before bump formation.

In step (f) of this method of manufacturing, it is preferred that ametallic thin film consisting of a metal different from the metal foil(in particular, a metal having an adhesiveness to the polyimideprecursor layer that is higher than the metal foil) is formed after theetching mask for bump formation is removed, and a polyimide precursorlayer to cover the bumps is formed on the metallic thin film layer. Inthis way, the adhesiveness with the polyimide precursor layer (and theimidized layer) can be improved.

The present invention also provides a method of manufacturing a wiringcircuit board having bumps in which the bumps formed on the wiringcircuit have a surface roughness on the tip face thereof of 0.2 to 20μm, the manufacturing method comprising the steps of:

(aa) laminating a protective film on the wiring circuit formationsurface of the metal foil which has a surface roughness of 0.2 to 20 μmand having a thickness which is the sum of a thickness of the wiringcircuit and a height of the bumps to be formed on the wiring circuit,and forming an etching mask for bump formation on a bump formationsurface of the metal foil;

(bb) half etching the metal foil from the side of the etching mask forbump formation to form bumps of the desired height;

(cc) forming a polyimide precursor layer to cover the bumps afterremoving the etching mask for bump formation:

(dd) half etching the polyimide precursor layer and imidizing the sameto form an insulating layer with a desired thickness;

(ee) forming an etching mask for wiring circuit formation on a wiringcircuit formation surface after removing the protective film provided onthe wiring circuit formation surface of the metal foil;

(ff) half etching the metal foil from the side of the etching mask forwiring circuit formation to form a wiring circuit with the desiredthickness: and

(gg) providing a cover coat layer on the wiring circuit after removingthe etching mask for wiring circuit formation. In this method ormanufacturing, the bumps are formed before the wiring circuit.

In step (cc) of this method of manufacturing, it is preferred that ametallic thin film consisting of a metal different from the metal foil(in particular, a metal having an adhesiveness to the polyimideprecursor layer that is higher than the metal foil) is formed after theetching mask for bump formation is removed, and a polyimide precursorlayer which covers the bumps is formed on the metallic thin film layer.In this way, the adhesiveness with the polyimide precursor layer (andthe imidized layer) can be improved.

In addition, the present invention provides a method of forming bumpswhich are formed integrally with a wiring circuit in one metal foil,wherein the bumps has a surface roughness on the tip faces thereof of0.2 to 20 μm, comprising the steps of:

forming an etching mask for bump formation on a bump formation surfaceof a metal foil which has a surface roughness of 0.2 to 20 μm and has athickness which is the sum of a thickness of the wiring circuit and aheight of the bumps to be formed on the wiring circuit: and

half etching the metal foil from the side of the etching mask for bumpformation to a depth which corresponds to the desired height for thebumps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1G are diagrams of the steps of a method of manufacturing awiring circuit board having bumps of the present invention;

FIGS. 2A to 2C are diagrams of the steps of a method of manufacturing awiring circuit board having bumps of the present invention;

FIG. 3 is a cross-section of an example of a wiring circuit board havingbumps of the present invention; and

FIGS. 4A and 4B are diagrams of the steps of a bump formation method;and

FIGS. 5A to 5E are diagrams of the steps of a conventional method ofmanufacturing a wiring circuit board having bumps.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Each step in the process of manufacturing a wiring circuit board havingbumps according to the present invention will be described in detailwhile referring to the Figures.

First, each step in the process of manufacturing a wiring circuit boardhaving bumps in which the bumps are formed on the wiring circuit, andthe process of manufacturing the wiring circuit before bump formation,will be described while referring to FIGS. 1A to 1G (steps (a) to (g)).

Step (a)

First, a protective film 4 is laminated onto a bump formation surface 3a of a metal foil 3, the metal foil 3 having a thickness that is the sumof a thickness t1 of a wiring circuit 1 (referred to with dotted linesin the FIG. 1A) and a height t2 of bumps 2 (referred to with dottedlines in the FIG. 1A) to be formed on wiring circuit 1. An etching maskfor wiring circuit formation 5 is formed on a wiring circuit formationsurface 3 b of metal foil 3 (FIG. 1A).

Here, metal foil 3 employs a bump formation surface 3 a that has asurface roughness of 0.2 to 20 μM, preferably 2 to 18 μm. By employing ametal foil 3 with this type of surface roughness, the surface roughnessof the tip faces of bumps 2 can be made to be 0.2 to 20 μm, andpreferably 2 to 18 μm. With bumps 2 having this type of surfaceroughness, because there are a large number of minute concave and convexportions formed on the tip faces (connecting surfaces), when an adhesiveis used and another electronic component (connected member) is connectedthereto, adhesive can be eliminated from the convex portions(protuberances). In addition, a highly reliable connection is madepossible because a plurality of convex portions are in contact with theconnected member.

Measurement of surface roughness can be done by using a commerciallyavailable surface roughness meter.

The optimal values for the thickness t1 of wiring circuit 1 and theheight t2 of bumps 2 are selected in accordance with the purpose forwhich the wiring circuit board is to be used. For example, when thewiring circuit board will be used as a mount for a semiconductor device,the thickness t1 of wiring circuit 1 can be set to 20 μm, the height t2of bumps 2 can be set to 30 μm, and the diameter of bumps 2 can be setto 50 μm.

In addition, the material used for the conducting layer in the wiringcircuit board can be used as the material for metal foil 3, and copperfoil can be preferably mentioned.

Etching mask 5 for wiring circuit formation can be formed on the wiringcircuit formation surface 3 b of metal foil 3 by screen printing aresist ink thereon. Alternatively, etching mask 5 for wiring circuitformation can also be formed by providing a photosensitive resin layer,a dry film or the like, and patterning by exposing and developingaccording to conventional methods.

Step (b)

Next, the metal foil 3 from the etching mask 5 for wiring circuitformation side is half etched to form the desired thickness t1 of wiringcircuit 1 (FIG. 1B).

The half etching conditions (temperature, etching fluid composition, andthe like) can be appropriately selected in accordance with thecomposition of metal foil 3, the thickness of the etching to beperformed, and the like.

Step (c)

Next, after removing etching mask for wiring circuit formation 5according to conventional methods, a cover coat layer 6 is provided onwiring circuit 1 (FIG. 1C).

Cover coat layer 6 can be formed by screen printing a coating materialused for a cover coat layer. Alternatively, it can also be formed byproviding a photosensitive resin layer, a dry film ox the like, andpatterning by exposing and developing according to conventional methods.In addition, it can also be formed by providing A layer formed of apolyimide precursor such as polyamic acid or the like, and patterningand imidization.

Step (d)

After removing protective film 4 provided on bump formation surface 3 aof metal foil 3 according to conventional methods, an etching mask forbump formation 7 is formed on bump formation surface 3 a (FIG. 1D)

Etching mask for bump formation 7 can be formed by screen printing aresist ink on bump formation surface 3 a of metal foil 3. Alternatively,etching mask for bump formation 7 can also be formed by providing aphotosensitive resin layer, a dry film or the like, and patterning byexposing and developing according to conventional methods.

Step (e)

Next, the metal foil 3 from the etching mask for bump formation 7 sideis half etched to form the desired height t2 of bumps 2 (FIG. 1E). Thedegree of surface roughness of the tip faces of bumps 2 formed therebycorresponds to the surface roughness of metal foil 3, and is thus 0.2 to20 μm.

The half etching conditions (temperature, etching fluid composition, andthe like) can be appropriately selected in accordance with thecomposition of metal foil 3, the thickness of the etching to beperformed, and the like.

Furthermore, cover coat layer 6 may be covered with a protective filmbefore half etching takes place (not shown in the Figure).

After removing etching mask for bump formation 7 according toconventional methods, a polyimide precursor layer 8 is formed in orderto cover bumps 2 (FIG. 1F).

In the event that a protective film covers cover coat layer 6, theprotective film may also be removed at the same time etching mask forbump formation 7 is removed.

In addition, polyimide precursor layer 8 can be formed by depositingpolyamic acid or the like according to conventional methods. Theimidization conditions also can be determined in accordance with thetype of polyimide precursor and the like used.

Furthermore, in Step (f), after the etching mask for bump formation isremoved, a metallic thin film layer consisting of a metal different fromthat of the metal foil is formed in order to improve the adhesivestrength between the metal foil and the insulating layer. It ispreferred that the polyimide precursor layer used to cover the bumps beformed on top of the metallic thin film layer. In this way, theadherence of the polyimide precursor layer (and the imidized polyimidelayer) can be improved.

For the metallic thin film layer, it is preferred that it be formed froma metal exhibiting an adhesive strength to the latex mentioned polyimideprecursor layer 8 that is higher than metal foil 3. In this way, theadhesiveness between polyimide precursor layer B and metal foil 3 can beenhanced, and thus, when undergoing chemical treatment (for example, theetch back treatment of polyimide precursor layer 8 in Step (g) and thelike), the occurrence of peeling phenomena between metal foil 3 andpolyimide precursor layer 8 or imidized insulating layer 9 can beprevented.

A thin film of Ni, Zn, Sn, or a Ni—Co alloy is preferably mentioned forthis type of metallic thin film in the event that metal foil 3 is aconventional copper foil. These thin films can be formed by theelectroless plating method, the electrolytic plating method, the vacuumevaporation method, and the like.

If the metallic thin film layer is too thin, the adhesiveness betweeninsulating layer 9 and wiring circuit 1 cannot be sufficiently improved,and if it is too thick, no effect corresponding to the added thicknesscan be obtained. Thus, the thickness of the metallic thin film layer ispreferably 0.01 to 4 μm. In particular, when the metallic thin filmlayer is a thin film of Zn or Sn, it is preferably 0.1 to 0.5 μm inthickness, when it is a thin film of a Ni—Co alloy, it is preferably 0.1to 4 μm in thickness, and when it is a thin film of Ni, it is preferably0.01 to 0.5 μm in thickness.

Step (g)

Polyimide precursor layer 8 is etch backed and imidized to form aninsulating layer 9 with a desired thickness t3, whereby a wiring circuitboard having bumps as shown in FIG. 1G is obtained.

Next, each step in the process of manufacturing a wiring circuit boardhaving bumps in which the bumps are formed on top of the wiring circuit,and the process of manufacturing the bumps before wiring circuitformation, will be described while referring to FIGS. 2A to 2G (Steps(aa) to (gg)). Furthermore, the reference numerals used in FIGS. 2A to2G that are the same as those used in FIGS. 2A to 2G refer to the sameelements as in FIGS. 1A to 1G.

Step (aa)

First, a protective film 4 is laminated onto a wiring circuit formationsurface 3 b of a metal foil 3, the metal foil 3 having a thickness thatis the sum of a thickness t1 of a wiring circuit 1 (referred to withdotted lines in the Figure) and a height t2 of bumps 2 (referred to withdotted lines in the Figure) to be formed on wiring circuit 1. An etchingmask for bump formation 7 is formed on a bump formation surface 3 a ofmetal foil 3 (FIG. 2A).

Here, metal foil 3 employs a bump formation surface 3 a that has asurface roughness of 0.2 to 20 μm, preferably 2 to 18 μm.

Step (bb)

Next, the metal foil 3 from the etching mask for bump formation 7 sideis half etched to form the desired thickness t2 of bumps 2 (FIG. 2B).The degree of surface roughness of the tip faces of bumps 2 formedthereby correspond to the surface roughness of metal foil 3, and thus is0.2 to 20 μm.

Step (cc)

After removing etching mask for bump formation 7 according toconventional methods, a polyimide precursor layer 8 is formed whichcovers bumps 2 (FIG. 2C).

Furthermore, in Step (cc), after removing the etching mask for bumpformation, it is preferred that a metallic thin film layer consisting ofa metal different from the metal foil be formed, and a polyimideprecursor layer for covering the bumps be formed on the metallic thinfilm layer (as referring to Step (f)).

Step (dd)

Polyimide precursor layer 8 is etch backed and imidized to form aninsulating layer 9 with a desired thickness t3 (FIG. 2D)

Step (ee)

After removing protective film 4 provided on wiring circuit formationsurface 3 b of metal foil 3 according to conventional methods, anetching mask for wiring circuit formation 5 is formed on wiring circuitformation surface 3 b (FIG. 2E).

Step (ff)

Next, the metal foil 3 from etching mask for wiring circuit formation 5side is half etched to form the desired thickness t1 of wiring circuit 1(FIG. 2F).

Furthermore, a protective film may be used to cover bumps 2 before halfetching occurs.

Step (gg)

After etching mask for wiring circuit formation 5 is removed accordingto conventional methods, a cover coat layer 6 is provided on wiringcircuit 1. In this way, the wiring circuit board having bumps shown inFIG. 2G can be obtained.

Furthermore, in the event that a protective film covers bumps 2, theprotective film may also be removed at the same time etching mask forwiring circuit formation 5 is removed.

As shown in FIG. 1G and FIG. 2G, the wiring circuit board having bumpsobtained by the aforementioned manufacturing method of the presentinvention has cover coat layer 6 formed on one side of wiring circuit 1,insulating layer 9 formed on the other side thereof, and bumps 2 incontinuity with wiring circuit 1 formed such that they project out frominsulating layer 9. However, the height of a plurality of bumps can bemade uniform because wiring circuit 1 and bumps 2 are formed integrallyfrom one metal foil. In addition, a constant bump connection is possiblebecause a large number of protrusions are formed on the tip faces ofbumps 2, and complex operations such as plating pre-treatment becomeunnecessary. Furthermore, because cover coat layer 6 has connector ports11 for allowing access to wiring circuit 1 from the cover coat layerside, the wiring circuit board having bumps becomes a double sidedaccess board, and can contribute to an increase in the packaging densityof electronic devices.

In addition, as shown in FIG. 3, when a metallic thin film 10 consistingof a metal different from the metal toil is provided between the bumpformation surface of wiring circuit 1 and insulating substrate 9, it ispossible to improve the adhesiveness of insulating layer 9. Inparticular, when insulating layer 9 is a polyimide layer imidized from apolyimide precursor layer, it is preferred that metallic thin film layer10 is formed from a material exhibiting an adhesive strength to thepolyimide precursor layer that is higher than the metal foil. Forexample, when the metal foil is a copper foil, the thin film is formedfrom Ni, Zn, Sn, or a Ni—Co alloy and the like. By constructing themetallic thin film layer in this manner, the adhesiveness between thepolyimide precursor layer and the metal foil can be enhanced, and thus,when undergoing chemical treatment (for example, the etch back treatmentof the polyimide precursor layer and the like), the occurrence ofpeeling phenomena between the metal foil and polyimide precursor layeror the imidized insulating layer 9 can be prevented.

Furthermore, the bump formation method described in FIGS. 4A and 4B canbe derived from the manufacturing method for the wiring circuit boardhaving bumps described in FIGS. 1A to 1G and FIGS. 2A to 2G when thebump formation method aspect thereof is clearly understood.

Specifically, as shown in FIG. 4B, bumps 2 having a tip face roughnessof 0.2 to 20 μm can be formed by forming an etching mask for bumpformation 7 on bump formation surface 3 a of metal foil 3 having athickness (t1+t2) which is the sum of thickness t1 of wiring circuit 1and height t2 of bumps 2 to be formed on wiring circuit 1, in which thesurface roughness of the bump formation surface is 0.2 to 20 μm (FIG.4A), and half etching metal toil 3 from the etching mask for bumpformation 7 side to a depth corresponding to the desired bump height t2.In this case, the process for forming wiring circuit 1 may occur afterthe formation of bumps 2, and the formation of bumps 2 may occur afterthe process for forming wiring circuit 1 has previously occurred.

In this way, the height of the bumps obtained thereby are uniform, andthe combined thickness of the wiring circuit and bumps are constant.Thus, a stable bump connection is made possible.

According to the manufacturing method of the present invention, a wiringcircuit board having bumps can be provided in which bump strength isstable, stable bump connections are possible, and complex operationssuch as plating pre-treatment are unnecessary. In particular, bumpconnections on integrated circuits can be stably connected in one batchby means of ultrasound.

The entire disclosure of the specification, summary, the claims anddrawings of Japanese Patent Application No. 2000-303745 filed on Oct. 3,2000 is hereby incorporated by reference.

What is claimed is:
 1. A wiring circuit board having bumps in which acover coat layer is formed on a first side of a wiring circuit, aninsulating layer is formed on a second side of the wiring circuit, andbumps in continuity with the wiring circuit are formed such that theyproject from said insulating layer, wherein the wiring circuit and bumpsare integrally formed from one metal foil, and a surface roughness ofthe tip faces of the bumps is 0.2 to 20 μm; the cover coat layer has aconnection aperture which allows access to the wiring circuit from thecover coat side; and peripheries of the wiring circuit at the connectionaperture are covered with the cover coat layer.
 2. The wiring circuitboard having bumps according to claim 1, wherein a metallic thin filmlayer consisting of a metal different from the metal foil is providedbetween a bump formation surface of the wiring circuit and theinsulating layer.
 3. The wiring circuit board having bumps according toclaim 2, wherein the insulating layer is a polyimide layer imidized froma polyimide precursor layer, and the metallic thin film layer exhibitsan adhesive strength to the polyimide precursor layer that is higherthan the metal foil.